Troubleshooting Windows Update Issues with VistaApril 21, 2008 – 6:10 PM
If you are having problems getting certain updates installed on Vista, there are two places you can look to troubleshoot:
%windir%\windowsupdate.log, a log file for Windows Update events
%windir%\Logs\CBS\CBS.log, a log file that tracks events to the servicing stack
These log files include the following fields: Time/Date Stamp, Message Severity, Message Source, Operation Type, and Main Text.
Source: Windows Networking